Lossless switch for radio frequency front-end module

ABSTRACT

An integrated front-end module (FEM) includes at least one power amplifier (PA) coupled to an antenna without inclusion of a switching element in a transmit signal path in the FEM between an output of the PA and the antenna. The FEM further includes at least one low-noise amplifier (LNA) and a switching circuit coupled in a receive signal path of the FEM between the antenna and an input of the LNA. The switching circuit is configured in a first mode to disable the PA and to connect the input of the LNA to the antenna for receiving signals from the antenna. The switching circuit is configured in a second mode to disconnect the input of the LNA from the antenna and to enable the PA for transmitting signals to the antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 15/398,774 filed Jan. 5, 2017, entitled “Lossless Switch for RadioFrequency Front-End Module,” the complete disclosure of which isexpressly incorporated herein by reference in its entirety for allpurposes.

FIELD

The present invention relates generally to the electrical, electronicand computer arts, and, more particularly, to switching circuitry forintegrated front-end modules.

BACKGROUND

High-performance wireless (e.g., Wi-Fi, WiMAX, etc.) router and/ornetworking applications, such as, for example, multiple-inputmultiple-output (MIMO) 4×4 systems, generally employ a front-end module(FEM) which comprises one or more power amplifiers (PAs) and one or morelow noise amplifiers (LNAs). The PA is employed to transmit radiofrequency (RF) signals to an antenna, and the LNA is employed to receiveRF signals from the antenna; an RF switch is utilized to selectivelycouple the antenna to either the PA or the LNA.

In many cases, there will be an insertion loss (typically in a range ofabout 0.2 decibels (dB) to 2.5 dB, or higher) attributable to the RFswitch, which is undesirable; this insertion loss generally increaseswith increasing power and/or frequency. Although there are some knownsolutions for reducing switch insertion loss in the RF front-end moduleusing complementary metal-oxide-semiconductor (CMOS) technology, suchsolutions are limited to low-power applications due to poor efficiency.For high-performance front-end modules, the technology used to fabricatethe PA is based on a gallium arsenide (GaAs) substrate, while thetechnology used to fabricate the LNA is based on a CMOS siliconsubstrate, and the RF switch is typically fabricated on asilicon-on-insulator (SOI) or silicon-on-sapphire (SOS) substrate or asa micro-electromechanical systems (MEMS) device. The different materialsand technologies, however, make it particularly challenging to integratethe various front-end components on the same substrate.

SUMMARY

One or more embodiments of the present invention provide techniques forconnecting a power amplifier (PA) to an antenna in a transmit signalpath of a front-end module (FEM) without insertion loss, whilemaintaining excellent isolation between the transmit signal path and areceive signal path in the FEM.

In accordance with one embodiment, an integrated FEM includes at leastone PA coupled to an antenna without inclusion of a switching element ina transmit signal path in the FEM between an output of the PA and theantenna. The FEM further includes at least one LNA and a switchingcircuit coupled in a receive signal path of the FEM between the antennaand an input of the LNA. The switching circuit is configured in a firstmode to disable the PA and to connect the input of the LNA to theantenna for receiving signals from the antenna. The switching circuit isfurther configured in a second mode to disconnect the input of the LNAfrom the antenna and to enable the PA for transmitting signals to theantenna.

In accordance with another embodiment, an integrated circuit includes asemiconductor substrate and at least one FEM formed on the substrate.The FEM includes at least one PA coupled to an antenna without inclusionof a switching element in a transmit signal path between an output ofthe PA and the antenna. The FEM further includes at least one LNA and aswitching circuit coupled in a receive signal path between the antennaand an input of the LNA. The switching circuit is configured in a firstmode to disable the PA and to connect the input of the LNA to theantenna for receiving signals from the antenna. The switching circuit isconfigured in a second mode to disconnect the input of the LNA from theantenna and to enable the PA for transmitting signals to the antenna.

Techniques according to embodiments of the present invention providesubstantial beneficial technical effects. By way of example only andwithout limitation, one or more embodiments provide techniques forforming a lossless switch for use in an RF FEM having one or more of thefollowing advantages, among other benefits:

-   -   reduces or eliminates insertion loss due to the RF switch in the        signal path between the PA and the antenna in the FEM;    -   enables integration of the RF FEM in a single die, thereby        reducing the solution size;    -   improves linearity in the FEM;    -   enables high isolation in both transmit and receive signal paths        at low and high frequencies;    -   reduces overall power consumption in the FEM;    -   improves reliability of the FEM;    -   provides a silicon-based technology which is fully integratable        with CMOS-based functional blocks to achieve system-on-chip        (SOC);    -   reduces the overall cost of the RF FEM.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are presented by way of example only and withoutlimitation, wherein like reference numerals (when used) indicatecorresponding elements throughout the several views, and wherein:

FIGS. 1A and 1B are a simplified block diagrams which conceptuallyillustrate exemplary front-end modules (FEMs) which can be modified toimplement aspects of the present invention;

FIG. 2 is a schematic diagram depicting at least a portion of anexemplary FEM, according to an embodiment of the present invention;

FIG. 3 is a schematic diagram depicting at least a portion of anexemplary FEM including filter and impedance matching circuitry,according to an embodiment of the present invention;

FIG. 4A is a schematic diagram depicting at least a portion of anexemplary FEM which provides enhanced isolation, according to anotherembodiment of the present invention;

FIG. 4B is a schematic diagram depicting at least a portion of anexemplary FEM which includes multiple receiver stages, according to anembodiment of the present invention;

FIG. 5 is a cross-sectional view depicting at least a portion of anexemplary power LDMOS transistor device suitable for use in an FEM,according to an embodiment of the invention; and

FIG. 6 is a cross-sectional view depicting at least a portion of anexemplary layout of the LDMOS transistors M0 and M1 in the illustrativeRF switch shown in FIG. 2, according to an embodiment of the invention.

It is to be appreciated that elements in the figures are illustrated forsimplicity and clarity. Common but well-understood elements that may beuseful or necessary in a commercially feasible embodiment may not beshown in order to facilitate a less hindered view of the illustratedembodiments.

DETAILED DESCRIPTION

Principles of the present invention will be described herein in thecontext of illustrative radio frequency (RF) front-end modules (FEMs)including improved switching circuitry for providing a losslessconnection between an antenna and a power amplifier (PA) in a transmitsignal path of the FEM, while maintaining superior isolation between thetransmit signal path and a receive signal path in the FEM. It is to beappreciated, however, that the invention is not limited to the specificdevices and fabrication methods illustratively shown and describedherein. Rather, aspects of the present disclosure relate more broadly totechniques for forming a lossless RF switch for use in an FEM. Moreover,it will become apparent to those skilled in the art given the teachingsherein that numerous modifications can be made to the embodiments shownthat are within the scope of the claimed invention. That is, nolimitations with respect to the embodiments shown and described hereinare intended or should be inferred.

For the purpose of describing and claiming embodiments of the invention,the term MISFET as may be used herein is intended to be construedbroadly and to encompass any type of metal-insulator semiconductorfield-effect transistor. The term MISFET is, for example, intended toencompass semiconductor field-effect transistors that utilize an oxidematerial as their gate dielectric (i.e., metal-oxide semiconductorfield-effect transistors (MOSFETs)), as well as those that do not. Inaddition, despite a reference to the term “metal” in the acronyms MISFETand MOSFET, the terms MISFET and MOSFET are also intended to encompasssemiconductor field-effect transistors wherein the gate is formed from anon-metal, such as, for instance, polysilicon; the terms “MISFET” and“MOSFET” are used interchangeably herein.

Although the overall fabrication method and devices formed thereby, aswill be described in further detail herein below, are entirely novel,certain individual processing steps required to implement a portion orportions of the method(s) according to one or more embodiments of theinvention may utilize conventional semiconductor fabrication techniquesand conventional semiconductor fabrication tooling. These techniques andtooling will already be familiar to one having ordinary skill in therelevant arts. Moreover, many of the processing steps and tooling usedto fabricate semiconductor devices are also described in a number ofreadily available publications, including, for example: P. H. Hollowayet al., Handbook of Compound Semiconductors: Growth, Processing,Characterization, and Devices, Cambridge University Press, 2008; and R.K. Willardson et al., Processing and Properties of CompoundSemiconductors, Academic Press, 2001, which are hereby incorporated byreference herein. It is emphasized that while some individual processingsteps are set forth herein, those steps are merely illustrative and oneskilled in the art may be familiar with several equally suitablealternatives that would also fall within the scope of the presentinvention.

It is to be understood that the various layers and/or regions shown inthe accompanying figures are not necessarily drawn to scale.Furthermore, one or more semiconductor layers of a type commonly used insuch integrated circuit (IC) devices may not be explicitly shown in agiven figure for economy of description. This does not imply, however,that the semiconductor layer(s) and/or region(s) not explicitly shownare omitted in the actual integrated circuit device.

As previously stated, high-performance wireless applications, such as,for example, multiple-input multiple-output (MIMO) 4×4 systems,generally employ an FEM which includes one or more PAs and one or moreLNAs coupled to an antenna through an RF switch. The PA is employed totransmit RF signals to the antenna and the LNA is employed to receive RFsignals from the antenna. FIGS. 1A and 1B are a simplified blockdiagrams which conceptually illustrate exemplary front-end modules(FEMs) which can be modified to implement aspects of the presentinvention.

With reference to FIG. 1A, an FEM 100 comprises a PA 102, which may bepart of transmitter circuitry 104 in a transmit signal path of the FEM,and an LNA 106, which may be part of receiver circuitry 108 in a receivesignal path of the FEM. The PA 102 is configured to transmit RF signalsto an antenna 110, and the LNA 106 is employed to receive RF signalsfrom the antenna. An RF switch 112 coupled to the antenna 110 isutilized to switch a connection of the antenna between the PA 102 andthe LNA 106. The RF switch 112 functions primarily to allow thetransmitter circuitry 104 and receiver circuitry 108 to share a singleantenna 110. The RF switch 112 is represented symbolically in FIG. 1 asa single-pole double throw (SPDT) switch, although variousimplementations of the RF switch are contemplated in accordance withaspects of the invention, some of which will be described in furtherdetail below. It is to be appreciated that in a conventional FEMimplementation, the PA 102, LNA 106 and RF switch 112 are usually notintegrated on the same substrate (e.g., silicon), according to one ormore embodiments. Advantageously, one or more embodiments of theinvention integrate a PA, LNA and RF switch on the same substrate.

The FEM 100 is operative in at least two modes. In a first (transmit)mode of operation, the RF switch 112 is configured having its commonterminal (COM) connected to terminal A, whereby an output of the PA 102is electrically coupled with the antenna 110, through the RF switch, fortransmitting RF signals to the antenna, and an input of the LNA 106 isleft unconnected. In a second (receive) mode, the RF switch 112 isconfigured having its common terminal connected to terminal B, wherebythe input of the LNA 106 is electrically coupled with the antenna 110for receiving RF signals therefrom, and the output of the PA 102 is leftunconnected. In one or more embodiments of the present invention, morethan two modes of operation may be employed (e.g., Bluetooth mode) inthe FEM.

Ideally, the RF switch 112 exhibits zero insertion loss in the transmitsignal path while in the first mode of operation, and infinite isolationbetween transmit and receive signal paths while in the second mode ofoperation. However, in practice there is always at least some insertionloss attributable to an on-resistance of the transistors often used toimplement the RF switch 112, typically in a range of about 0.2 decibels(dB) to 2.5 dB or higher, and some finite signal leakage (e.g.,crosstalk), typically about −30 dB to about −25 dB at frequencies in thegigahertz (GHz) range, between the two terminals (A and B) of theswitch. Isolation can be improved by adding more switch stages, althoughdoing so increases the insertion loss. By way of example, FIG. 1B is aschematic diagram depicting a conventional solution of switchingdevices, where an illustrative FEM 150 includes an RF switch 152comprising a plurality of transistor switches connected in series inboth the transmit and receive signal paths of the FEM. Moreover, sincepower is proportional to a square of the current, and since the currentflowing in the transmit signal path will be much higher than the currentflowing in the receive signal path, the on-resistance of the transistorswitches will have a significantly greater detrimental impact on thetransmit signal path compared to the receive signal path.

Embodiments of the invention address one or more of the above-noteddisadvantages by providing an RF switch topology which affords a trulylossless connection between a PA and an antenna in a transmit signalpath of an FEM while maintaining superior isolation between the antennaand an LNA in a receive signal path of the FEM. By way of illustrationonly and without limitation or loss of generality, FIG. 2 is a schematicdiagram depicting at least a portion of an exemplary FEM 200, accordingto an embodiment of the invention. The FEM 200, in this embodiment,comprises a multi-stage PA including a first PA (PA1) 202 and a secondPA (PA2) 204, which may be part of transmitter circuitry 206, and an LNA208, which may be part of receiver circuitry 210. An output of the firstPA 202 is coupled to an input of the second PA 204 at a first node N1,and an output of the second PA 204 is coupled directly to an antenna 212at a second node N2, thereby beneficially eliminating the insertion lossassociated with an RF switch typically connected in series between thePA and the antenna. The PAs 202, 204 are preferably fabricated usingcircuit components (e.g., transistors) able to withstand high voltage(e.g., about 25 volts); that is, devices having a high breakdownvoltage. The LNA is preferably fabricated using the same technology asthe PAs so that it can be easily integrated with the PAs on the samesubstrate (e.g., silicon).

The FEM 200 further comprises an RF switch 214 connected between theantenna 212 and an input of the LNA 208 in a receive signal path of theFEM. The RF switch 214 is adapted to selectively couple the LNA to theantenna 212 as a function of one or more control signals supplied to theRF switch. In this embodiment, the RF switch 214 comprises a pair ofmetal-oxide semiconductor (MOS) devices. Specifically, the RF switch 214includes a first MOS device, M0, which may be an n-typelaterally-diffused metal-oxide semiconductor (LDMOS) field-effecttransistor (FET). A drain (D) of transistor M0 is connected with theantenna 212 and the output of the second PA 204 at node N2, a source (S)of M0 is connected with an input of the LNA 208 at a third node N3, anda gate (G) of M0 is adapted to receive a first control signal, CS1. TheRF switch 214 further includes a second MOS device, M1, which may alsobe an n-type LDMOSFET. A drain of transistor M1 is connected with theinput of the LNA 208 and source of transistor M0 at node N3, a source ofM1 is connected to ground, or an alternative voltage source (e.g., VSS),and a gate of M1 is adapted to receive a second control signal, CS2.Configured in this manner, transistor M0 functions as a pass device andtransistor M1 functions as a shunt device. The RF switch 214 ispreferably fabricated using circuit components (e.g., transistors)having a high breakdown voltage; preferably, the RF switch is fabricatedusing the same technology as the PAs 202, 204 and LNA 208 so that it canbe easily integrated with the PAs and LNA on the same substrate.

The FEM 200 is operative in one of at least two modes. In a first modeof operation, which may be referred to as a transmit mode, the RF switch214 is configured to disconnect the LNA 208 from the antenna 212, andthe PAs 202 and 204 are enabled for transmitting RF signals.Alternatively, in a second mode of operation, which may be referred toas a receive mode, the RF switch 214 is configured to connect the LNA208 to the antenna 212 and to disable one or both PAs 202, 204. In oneor more embodiments, at least the second PA 204 coupled with the antennais disabled so as not to inject RF signals into the LNA during thereceive mode of operation.

In order to selectively disable the second PA 204, the FEM 200, in oneor more embodiments, includes a third MOS device, M2, which may be ann-type LDMOSFET, connected between the input of the second PA andground. Specifically, a drain of transistor M2 is connected with theinput of the second PA 204 at node N1, a source of M2 is connected toground, and a gate of M2 is adapted to receive a third control signal,CS3. In this configuration, transistor M2 functions as a shunt device.Thus, when transistor M2 is turned on, such as, for example, when M2 isan n-type MOS (NMOS) device and the control signal CS3 supplied to M2 isat a high voltage level (e.g., VDD), the input of the second PA 204 isshunted to ground, thereby disabling the second PA. Transistor M2,although shown as being external to the RF switch 214, may, in one ormore embodiments, be implemented as part of the RF switch.Alternatively, in other embodiments, transistor M2 may be incorporatedinto the second PA 204 as part of a bias or enable circuit of the secondPA, such that when an appropriate level control signal is supplied tothe second PA, the bias circuit in the second PA is disabled, therebypreventing the second PA from passing RF signals supplied from theantenna 212.

An operation of the FEM 200 will now be described, according to one ormore embodiments of the invention, wherein it is assumed that alltransistors M0, M1, M2 are NMOS devices. Thus, an active high (e.g.,VDD) control signal CS1, CS2 or CS3 supplied to a given transistor M0,M1 or M2, respectively, will turn on (i.e., enable or activate) thetransistor. Similarly, an active low (e.g., VSS or ground) controlsignal supplied to a given one of the transistors will turn off (i.e.,disable or deactivate) the transistor. It is to be appreciated thatother types of circuit elements may be used to implement the pass andshunt switching devices, with or without modification of the controlsignal levels, as will become apparent to those skilled in the art. Forexample, one or more of transistors M0, M1 and M2 may be implementedusing a p-type MOS (PMOS) transistor, with a logical complement of thecorresponding control signal being used to enable/disable thetransistor; that is, an active low control signal is used to turn on thePMOS device and an active high control signal is used to turn off thedevice.

To receive RF signals in the second mode of operation of the FEM 200,transistor M2 is turned on, by applying an active high control signalCS3 to M2, thereby connecting the input of the second PA 204 (at nodeN1) to ground, or an alternative voltage source (e.g., VSS). With theinput of the second PA 204 shunted to ground, the second PA will bedisabled, thus effectively blocking RF signals from a preceding stage inthe transmitter 206 from being passed to the antenna 212, and viceversa. A bias circuit (not explicitly shown, but implied) in the secondPA 204 may also be disabled so as to reduce overall power consumption inthe FEM 200. Next, the shunt transistor M1 in the RF switch 214 isturned off, by applying an active low control signal CS2 to M1, so as toallow node N3 to float, and the pass transistor M0 is turned on, byapplying an active high control signal CS1 to M0, to connect the antenna212 to the input of the LNA 208 at node N3. The LNA 208 is enabled inthis mode, so RF signals received from the antenna 212 are amplified bythe LNA and passed to a subsequent stage in the receiver 210. Timing ofthe control signals CS1, CS2 and CS3 is preferably configured accordingto a prescribed order of activation and/or deactivation of the circuitcomponents (e.g., PAs, LNA, RF switch) in the FEM 200.

To transmit RF power signals to the antenna 212 in the first mode ofoperation of the FEM 200, the LNA 208 is first disabled. To accomplishthis, the pass transistor M0 in the RF switch 214 is turned off, byapplying an active low control signal CS1 to M0, thereby disconnectingthe input of the LNA 208 from the antenna 212, and the shunt transistorM1 is turned on, by applying an active high control signal CS2 to M1,thereby connecting the input of the LNA at node N3 to ground (or analternative voltage source). Next, the second PA 204 is enabled byturning on the bias circuit, which includes turning off transistor M2,by applying an active low control signal CS3 to M2, thereby allowing theinput to the second PA at node N1 to be defined by the output of thefirst PA 202. With the second PA 204 enabled, the transmitter 206 canpass RF power signals to the antenna 212. As previously explained, withthe output of the second PA 204 coupled to the antenna 212 without anyswitch element in the transmit signal path, there will be no power lossotherwise attributable to the RF switch.

As previously stated, active devices, such as the devices employed inthe PAs 202, 204, LNA 208 and RF switch 214, as well as any activedevices external to the primary functional circuits (e.g., transistorM2), are preferably transistors having a high breakdown voltage. For atleast this reason, the pass and shunt transistors (e.g., M0, M1, M2) inone or more embodiments are implemented using asymmetric devices, suchas diffused metal-oxide semiconductor (DMOS) FETs.

FIG. 3 is a schematic diagram depicting at least a portion of anexemplary FEM 300 including filter and impedance matching circuitry,according to another embodiment of the invention. The FEM 300 isessentially the same as the illustrative FEM 200 shown in FIG. 2, onlywith the addition of an impedance matching network 302, connected to theantenna 212, and filter circuitry, 304 and 306, connected in thetransmit and receive signal paths, respectively. The impedance matchingnetwork 302, in this embodiment, is coupled between the antenna 212 andnode N2. The matching network 302, in one or more embodiments, comprisespassive components (i.e., circuitry) which can be adjusted (i.e., tuned)to match the impedance of at least the second PA 204 for increasing,preferably maximizing, power delivery to the antenna 212. First filtercircuitry 304 is connected in the transmit signal path, between theoutput of the second PA 204 and the antenna matching network 302 at nodeN2. The first filter circuitry 304, which may comprise, for example, oneor more low-pass filters, band-pass filters, or other filter types, isconfigured to protect the receiver 210 from overload during RF signaltransmission, and may also provide signal processing (e.g., signalshaping, pre-distortion, etc.). Likewise, second filter circuitry 306 isconnected in the receive signal path, between the RF switch 214 and thematching network 302 at node N2. The second filter circuitry 306, whichmay comprise for example, one or more low-pass filters, band-passfilters, or other filter types, is configured to protect the preventunwanted emissions when receiving RF signals.

In order to provide improved isolation between the LNA and PA, two ormore RF switches can be stacked (i.e., connected in series). Withreference now to FIG. 4A, a schematic diagram depicts at least a portionof an exemplary FEM 400 which provides enhanced isolation, according toanother embodiment of the invention. The FEM 400, in this embodiment,like in the embodiment shown in FIG. 2, comprises a multi-stage PAincluding a first PA (PA1) 402 and a second PA (PA2) 404, which may forman output stage of transmitter circuitry 406, and an LNA 408, which maybe part of receiver circuitry 410. An output of the first PA 402 iscoupled to an input of the second PA 404 at a first node N1, and anoutput of the second PA 404 is coupled to an antenna 412 at a secondnode N2 without the inclusion of a switch element in the transmit signalpath between the PA and antenna, thus eliminating the insertion lossotherwise associated with an RF switch often connected between the PAand the antenna.

The FEM 400 further comprises an RF switch 414 connected between theantenna 412 and an input of the LNA 408 in a receive signal path of theFEM. The RF switch 414 is adapted to selectively couple the LNA to theantenna 412 as a function of one or more control signals supplied to theRF switch. In this illustrative embodiment, the RF switch 414 comprisesfour MOS transistors—two functioning as pass devices and two functioningas shunt devices—to provide enhanced isolation between the LNA 408 andthe PA 404. It is to be appreciated that embodiments of the inventionare not limited to the number of stages employed in the RF switch.

More particularly, the RF switch 414 includes a first MOS pass device,M0, a second MOS pass device, M1, a first MOS shunt device, M2, and asecond MOS shunt device, M3, each of which may comprise an n-typeLDMOSFET. A drain of transistor M0 is connected with the antenna 412 andthe output of the second PA 404 at node N2, a source of M0 is connectedwith drains of transistors M1 and M2 at a third node N3, and a gate ofM0 is adapted to receive a first control signal, CS1. A source oftransistor M1 is connected with an input of the LNA 408 and a drain oftransistor M3 at a fourth node N4, and a gate of M1 is adapted toreceive a second control signal, CS2. Sources of transistors M2 and M3are connected to ground, or an alternative voltage source (e.g., VSS), agate of M2 is adapted to receive a third control signal, CS3, and a gateof M3 is adapted to receive a fourth control signal, CS4. Like the RFswitch 214 shown in FIG. 2, the RF switch 414 is preferably fabricatedusing circuit components (e.g., transistors) having a high breakdownvoltage; preferably, the RF switch is fabricated using the sametechnology as the PAs 402, 404 and LNA 408 so that it can be easilyintegrated with the PAs and LNA on the same substrate.

The FEM 400 is operative in one of at least two modes. In a mannerconsistent with the FEM 200 depicted in FIG. 2, in a first mode ofoperation, which may be referred to as a transmit mode, the RF switch414 is configured to disconnect the LNA 408 from the antenna 412, andthe PAs 402 and 404 are enabled for transmitting RF signals.Alternatively, in a second mode of operation, which may be referred toas a receive mode, the RF switch 414 is configured to connect the LNA408 to the antenna 412 and to disable one or both PAs 402, 404. In thisembodiment, both the first and second PAs 402 and 404, respectively, aredisabled to provide improved isolation during the receive mode ofoperation compared to the FEM 200 of FIG. 2.

In order to selectively disable the first and second PAs, the FEM 400,in one or more embodiments, includes two MOS transistors functioning asshunt devices, each of which may comprise an n-type LDMOSFET. Moreparticularly, a third MOS shunt device, M4, is connected between theinput of the first PA 402 and ground, and a fourth MOS shunt device, M5,is connected between the input of the second PA 404 and ground.Specifically, a drain of transistor M4 is connected with the input ofthe first PA 404 at a fifth node N5, a source of M4 is connected toground, and a gate of M4 is adapted to receive a fifth control signal,CS5. Likewise, a drain of transistor M5 is connected with the output ofthe first PA 402 and the input of the second PA 404 at node N1, a sourceof M5 is connected to ground, and a gate of M5 is adapted to receive asixth control signal, CS6. When n-type LDMOS transistors M4 and M5 areturned on, such as, for example, when the control signals CS5 and CS6applied to M4 and M5, respectively, are at a high voltage level (e.g.,VDD), the inputs of the first and second PAs 402, 404 are shunted toground, thereby disabling the PAs. Transistors M4 and M5, although shownas being external to the RF switch 414, may, in one or more embodiments,be implemented as part of the RF switch. Alternatively, in otherembodiments, transistors M4 and M5 may be incorporated into acorresponding PA as part of a bias or enable circuit of the PA, suchthat when an appropriate level control signal is applied to the PAs, thebias circuits in the first and second PAs are disabled, therebypreventing the PA from passing RF signals supplied thereto to theantenna 412.

An operation of the FEM 400 will be consistent with the operation of theFEM 200 previously described in conjunction with FIG. 2, except for theadditional control signals in the RF switch 414 and transmitter 406.Specifically, in one or more embodiments, to receive RF signals in thesecond mode of operation of the FEM 400, transistors M4 and M5 areturned on, by applying active high control signals CS5 and CS6 to M4 andM5, respectively, thereby connecting the input of the first PA 402, atnode N5, and the input of the second PA 404, at node N1, to ground, oran alternative voltage source (e.g., VSS). In one or more embodiments,the shunt devices M4 and M5 are turned on at the same time, and thuscontrol signals CS5 and CS6 may be implemented using the same signal. Inone or more alternative embodiments, a delay may be introduced betweendisabling of the first and second PAs, in which case the control signalsCS5 and CS6 will be different relative to one another (although the twosignals may still share a common generation source, such as, forexample, being different phases of a common clock signal). With theirinputs shunted to ground, the PAs 402, 404 will be disabled, thuseffectively blocking RF signals from a preceding stage in thetransmitter 406 from being passed to the antenna 412, and vice versa.One or more bias circuits (not explicitly shown, but implied) in thefirst and second PAs 402, 404 may also be disabled so as to reduceoverall power consumption in the FEM 400.

Next, the shunt transistors M2 and M3 in the RF switch 414 are turnedoff, such as by applying active low control signals CS3 and CS4 to M2and M3, respectively, so as to allow nodes N3 and N4 to float. In one ormore embodiments, the shunt devices M2 and M3 are turned off at the sametime, and thus control signals CS3 and CS4 may be implemented using thesame signal. In one or more other embodiments, a delay may be introducedbetween disabling of transistors M2 and M3, in which case the controlsignals CS3 and CS4 will be different relative to one another. The passtransistors M0 and M1 are turned on, such as by applying active highcontrol signals CS1 and CS2 to M0 and M1, respectively, to couple theantenna 412 to the input of the LNA 408. The two pass devices M0 and M1provide multiple stages of isolation between the LNA 408 and the PAs402, 404. The LNA 408 is enabled in this mode, so RF signals receivedfrom the antenna 412 are amplified by the LNA and passed to a subsequentstage in the receiver 410. Timing of the control signals CS1 through CS6is preferably configured according to a prescribed order of activationand/or deactivation of the circuit components (e.g., PAs, LNA, RFswitch) in the FEM 400.

It is to be appreciated that the insertion loss introduced by theadditional pass device stage in the RF switch 414 will be insignificantdue, at least in part, to the low current flowing through the passdevices in the receive signal path. In some applications, the higherisolation (i.e., lower noise) performance benefit achieved through theuse of multiple RF switch stages will far outweigh any increase ininsertion loss in the receive signal path. More critical is thebeneficial elimination of switch elements in the transmit signal path,according to embodiments of the invention, since there will generally bea larger current flowing in the transmit signal path.

Similarly, to transmit RF power signals to the antenna 412 in the firstmode of operation of the FEM 400, the LNA 408 is first disabled. Toaccomplish this, the pass transistors M0 and M1 in the RF switch 414 areturned off, by applying an active low control signals CS1 and CS2 to M0and M1, respectively, thereby disconnecting the input of the LNA 408from the antenna 412. The shunt transistors M2 and M3 are turned on,such as by applying active high control signals CS3 and CS3 to M2 andM3, respectively, thereby connecting the input of the LNA at node N4 toground (or an alternative voltage source). The PAs 402 and 404 are thenenabled by turning on the bias circuit in each of the PAs, whichincludes turning off shunt transistors M4 and M5, such by applyingactive low control signal CS5 and CS6 to M4 and M5, respectively. In oneor more embodiments, the shunt devices M4 and M5 are turned off at thesame time, and thus control signals CS5 and CS6 may be implemented usingthe same signal. In one or more other embodiments, a delay may beintroduced between disabling of the transistors M4 and M5, in which casethe control signals CS5 and CS6 will be different relative to oneanother. With the first and second PAs 402, 404 enabled, the transmitter406 can pass RF power signals to the antenna 412. As previously stated,without any switch element in the transmit signal path between thesecond PA 404 and the antenna 412, there will be no power loss otherwiseattributable to the RF switch.

The table below provide a summary of the status of the transistors inthe RF switch 414 and transmitter 406 for both transmit and receivemodes of operation in the FEM 400, according to one or more embodimentsof the invention.

Transmit Mode Receive Mode M0 Off On M1 Off On M2 On Off M3 On Off M4Off On M5 Off On

While a receiver including only a single LNA is shown in FIGS. 2 and 4A,aspects of the invention are similarly applicable to a receiver havingmultiple LNAs. By way of example only, FIG. 4B is a schematic diagramdepicting at least a portion of an exemplary FEM 450 which includesmultiple receiver stages, according to an embodiment of the invention.The FEM 450 is essentially the same as FEM 400 shown in FIG. 4A, exceptfor the inclusion of an addition LNA and corresponding switch circuitry.Specifically, focusing on the receive signal path, the exemplary FEM 450comprises a receiver 452 which includes a first LNA 408 and a second LNA454. In one or embodiments, the first and second LNAs 408, 454 may beidentical to one another or, in other embodiments, the first and secondLNAs may be different (e.g., different gains, impedance, etc.).

The FEM 450 further comprises an RF switch 456 connected between theantenna 412 and an input of each of the LNAs 408 and 454 incorresponding receive signal paths of the FEM. The RF switch 456 isconfigured to selectively couple the LNAs 408 and 454 to the antenna 412as a function of corresponding control signals supplied to the RFswitch. In this illustrative embodiment, each receive signal path of theRF switch 456 comprises four MOS transistors—two functioning as passdevices and two functioning as shunt devices—to provide enhancedisolation, compared to the illustrative switch 214 shown in FIG. 2,between the corresponding LNAs 408, 454 and the PA 404. It is to beappreciated that embodiments of the invention are not limited to thenumber of stages employed in the RF switch.

More particularly, the RF switch 456 includes first switch circuitryconnected in a first receive signal path between the first LNA 408 andthe antenna 412, and second switch circuitry connected in a secondreceive signal path between the second LNA 454 and the antenna 412. Thefirst switch circuitry in the RF switch 456 is implemented consistentwith the RF switch 414 shown in FIG. 4A and includes a first MOS passdevice, M0, a second MOS pass device, M1, a first MOS shunt device, M2,and a second MOS shunt device, M3, each of which may comprise an n-typeLDMOSFET. A drain of transistor M0 is connected with the antenna 412 andthe output of the second PA 404 at node N2, a source of M0 is connectedwith drains of transistors M1 and M2 at a third node N3, and a gate ofM0 is adapted to receive a first control signal, CS1. A source oftransistor M1 is connected with an input of the first LNA 408 and adrain of transistor M3 at a fourth node N4, and a gate of M1 is adaptedto receive a second control signal, CS2. Sources of transistors M2 andM3 are connected to ground, or an alternative voltage source (e.g.,VSS), a gate of M2 is adapted to receive a third control signal, CS3,and a gate of M3 is adapted to receive a fourth control signal, CS4.

Similarly, the second switch circuitry in the RF switch 456 includes afirst MOS pass device, M6, a second MOS pass device, M7, a first MOSshunt device, M8, and a second MOS shunt device, M9, each of which maycomprise an n-type LDMOSFET. A drain of transistor M6 is connected withthe antenna 412 and the output of the second PA 404 at node N2, a sourceof M6 is connected with drains of transistors M7 and M8 at node N6, anda gate of M6 is adapted to receive a seventh control signal, CS7. Asource of transistor M7 is connected with an input of the second LNA 454and a drain of transistor M9 at node N7, and a gate of M7 is adapted toreceive an eighth control signal, CS8. Sources of transistors M8 and M9are connected to ground, or an alternative voltage source (e.g., VSS), agate of M8 is adapted to receive a ninth control signal, CS9, and a gateof M9 is adapted to receive a tenth control signal, CS10.

The control signals CS7-CS10 supplied to the second switch circuitry maybe different than the control signals CS1-CS4 supplied to the firstswitch circuitry in the RF switch 456, so that the first and secondswitch circuitry can be independently controlled. In other embodiments,the first and second switch circuitry in the RF switch 456 arecontrolled by the same set of control signals. In the latter embodiment,for example, control signals CS7 and CS1 are the same, control signalsCS8 and CS2 are the same, control signals CS9 and CS3 are the same, andcontrol signals CS10 and CS4 are the same. The operation of each of thefirst and second switch circuitry in the RF switch 456 is preferablyconsistent with the operation of the RF switch 414 previously describedin conjunction with FIG. 4A.

Like the RF switch 214 shown in FIG. 2, the RF switch 456 is preferablyfabricated using circuit components (e.g., transistors) having a highbreakdown voltage; preferably, the RF switch is fabricated using thesame technology as the PAs 402, 404 and LNAs 408, 454 so that it can beeasily integrated with the PAs and LNAs on the same substrate.

In one or more embodiments, one or more of the MOS transistors used inthe RF switch (e.g., RF switch 214, 414 or 456 shown in FIG. 2, 4A or4B, respectively) can be isolated from other circuit devices by using adeep n-type well or an n-type buried layer. By way of example only andwithout limitation, FIG. 5 is a cross-sectional view depicting at leasta portion of an exemplary power LDMOS transistor device 500 suitable foruse in an FEM, according to an embodiment of the invention. The LDMOSdevice 500 includes a substrate 502 which, in one or more embodiments,is formed of single-crystalline silicon (e.g., having a <100> or <111>crystal orientation). Suitable alternative materials for forming thesubstrate 502 may also be used, such as, but not limited to, germanium,silicon germanium, silicon carbide, gallium arsenide, gallium nitride,or the like. Additionally, in one or more embodiments the substrate 502is preferably modified by adding an impurity or dopant (e.g., boron,phosphorus, arsenic, etc.) to change a conductivity of the material(e.g., n-type or p-type). In one or more embodiments, where the LDMOSdevice 500 is an n-channel transistor, the substrate 502 is of p-typeconductivity and may thus be referred to as p-substrate (P-SUB). Ap-substrate may be formed by adding a p-type impurity or dopant (e.g.,Group III elements, such as boron) of a prescribed concentration level(e.g., about 10¹⁴ to 10¹⁹ atoms per cubic centimeter) to the substratematerial, such as by using a diffusion or implant step, to change theconductivity of the material as desired. In one or more alternativeembodiments, where the LDMOS device 500 is a p-channel transistor, ann-type substrate (N-SUB) may be formed by adding an n-type impurity ordopant (e.g., Group V elements, such as phosphorus) of a prescribedconcentration level to the substrate material.

The LDMOS device 500, in this embodiment, further includes a deep n-typewell or n-well (DNW) 504 formed in the substrate 502. As is known bythose skilled in the art, well formation, in one or more embodiments,typically includes oxidation of the wafer at high temperature (e.g.,about 1100° C.) to form an oxide layer (e.g., SiO₂) on the upper surfaceof the wafer. A photoresist layer is then deposited on the oxide layerand is patterned, using an n-well mask in a photolithographic process,and etched (e.g., using a wet etchant, such as hydrofluoric acid (HF))to create an opening through the oxide layer defining where the deepn-well 504 is to be formed. The n-well 504 is formed by adding an n-typeimpurity of a prescribed doping level to the underlying substrate 502through the n-well opening in the oxide layer, such as by diffusion orimplantation. The oxide layer is then stripped from the upper surface ofthe wafer and processing continues. A heavily-doped region 506 having aconductivity type the same as the deep n-well 504 is formed proximatethe upper surface of the substrate and within the deep n-well to form abody (B) contact of the LDMOS device 500.

A deep p-type well or p-well (DPW) 508 is formed within the n-well 504,proximate the upper surface of the substrate. The p-well 508, which isat a shallower depth compared to the deep n-well 504, may be formed in amanner consistent with the formation of the deep n-well 504, only ratherthan adding an n-type impurity, as in the case of the n-well, a p-typeimpurity of a prescribed doping level is added to a defined regionwithin the n-well to change the conductivity type. A p-n junctionbetween the deep p-well 508 and the deep n-well 504 is used to isolatethe structure from the substrate 502. The boundaries of the deep n-well504 and deep p-well 508 are shown as dotted lines, primarily because thewell boundaries are not necessarily sharp. Specifically, the p-njunction between the two wells is actually a depletion region, with thethicknesses of the n-well 504 and p-well 508 dependent on the dopantconcentrations of the respective n- and p-regions. The p-well 508 alsoserves as the well in which an NMOS transistor device is formed.

A body region 510, which in this embodiment is of p-type conductivity(p-body), is formed proximate the upper surface of the substrate 502 andwithin the deep p-well 508, starting from an edge of the deep p-well 504closest to a source side of the device and extending laterally toward adrain side of the device. The body region 510, in one or moreembodiments, is formed using a deep diffusion or implant step from thesource side, extending laterally to form a graded channel region 512 inthe device 500. A lightly-doped drain (LDD) region 514 is formedproximate the upper surface of the substrate 502 within the deep p-well508 and laterally adjacent to the p-body region 510. The LDD region 514if formed having a conductivity type which is opposite that of the bodyregion 510; in this embodiment, n-type conductivity.

Source and drain regions 516 and 518, respectively, are formed proximatethe upper surface of the substrate 502 and spaced laterally from oneanother; the source region being formed in the body region 510 and thedrain region being formed in the LDD region 514. The source and drainregions 516, 518 are preferably doped, such as by a conventional implantstep, with an impurity of a known concentration level to selectivelychange the conductivity of the material as desired. In one or moreembodiments, the source and drain regions 516, 518 have a conductivitytype associated therewith which is opposite a conductivity type of thedeep p-well 508, so that active regions can be formed in the device. Inthe embodiment shown in FIG. 5, the source and drain regions 516, 518are of n-type conductivity.

A thin dielectric layer 520 is formed on the upper surface of thesubstrate 502. The thin dielectric layer 520 may comprise an insulatingmaterial, such as, for example, silicon dioxide (SiO₂), that is grown ordeposited on the upper surface of the substrate to a desired thickness(e.g., about 50-400 angstroms). A gate 522, which, in one or moreembodiments, comprises a polycrystalline silicon (polysilicon) layer, isformed over the thin dielectric layer 520, such as, for example, using achemical vapor deposition (CVD) technique. The thin dielectric layer 520under the gate 522 is commonly referred to as “gate oxide,” since itoften comprises an oxide which electrically isolates the gate 522 fromthe drain and/or source regions of the device. The polysilicon layer isgenerally patterned using, for example, a conventional photolithographicprocess, and followed by an etching step (e.g., dry etching) to form thegate 520, as will be understood by those skilled in the art.

FIG. 6 is a cross-sectional view depicting at least a portion of anexemplary layout of the LDMOS transistors M0 and M1 in the illustrativeRF switch 214 shown in FIG. 2, according to an embodiment of theinvention. With reference to FIGS. 5 and 6, the LDMOSFETs in the deepn-well (DNW), or n-type buried layer (NBL), used in the RF switch 214are connected, in this embodiment, in the following manner. The sourceand body (B) of the pass transistor M0 are connected to the input of theLNA 208, while the drain of M0 is connected to the antenna 212 and theoutput of the PA 204. The drain of the shunt transistor M1 is connectedto the source of transistor M0, and the source and body of M1 areconnected to ground.

Given the discussion thus far, it will be appreciated that an exemplaryintegrated FEM includes at least one PA coupled to an antenna withoutinclusion of a switching element in a transmit signal path in the FEMbetween an output of the PA and the antenna. The FEM further includes atleast one LNA and a switching circuit coupled in a receive signal pathof the FEM between the antenna and an input of the LNA. The switchingcircuit is configured in a first mode to disable the PA and to connectthe input of the LNA to the antenna for receiving signals from theantenna. The switching circuit is further configured in a second mode todisconnect the input of the LNA from the antenna and to enable the PAfor transmitting signals to the antenna. In one or more embodiments, theswitching circuit includes at least a first pass transistor and at leasta first shunt transistor. The pass transistor is connected between theantenna and the input of the LNA and selectively connects the input ofthe LNA to the antenna as a function of a first control signal. Theshunt transistor is connected between the input of the LNA and a firstvoltage source and selectively connects the input of the LNA to thefirst voltage source as a function of a second control signal.

Given the discussion thus far, it will also be appreciated that anintegrated circuit includes a semiconductor substrate and at least oneFEM formed on the substrate. The FEM includes at least one PA coupled toan antenna without inclusion of a switching element in a transmit signalpath between an output of the PA and the antenna. The FEM furtherincludes at least one LNA and a switching circuit coupled in a receivesignal path between the antenna and an input of the LNA. The switchingcircuit is configured in a first mode to disable the PA and to connectthe input of the LNA to the antenna for receiving signals from theantenna. The switching circuit is further configured in a second mode todisconnect the input of the LNA from the antenna and to enable the PAfor transmitting signals to the antenna. In one or more embodiments, theintegrated circuit further includes a first well of a secondconductivity type formed in the substrate and proximate an upper surfaceof the substrate, and a second well of the first conductivity typeformed within the first well and proximate the upper surface of thesubstrate, the first well having a depth in the substrate that isgreater than a depth of the second well. A least one transistor includedin the switching circuit is formed in the second well, a p-n junctionbetween the first and second wells electrically isolating the transistorfrom the substrate.

At least a portion of the techniques of the present invention may beimplemented in an integrated circuit. In forming integrated circuits,identical die are typically fabricated in a repeated pattern on asurface of a semiconductor wafer. Each die includes a device describedherein, and may include other structures and/or circuits. The individualdie are cut or diced from the wafer, then packaged as an integratedcircuit. One skilled in the art would know how to dice wafers andpackage die to produce integrated circuits. Any of the exemplarycircuits illustrated in the accompanying figures, or portions thereof,may be part of an integrated circuit. Integrated circuits somanufactured are considered part of this invention.

Those skilled in the art will appreciate that the exemplary structuresdiscussed above can be distributed in raw form (i.e., a single waferhaving multiple unpackaged chips), as bare dies, in packaged form, orincorporated as parts of intermediate products or end products thatbenefit from having a lossless connection between a PA and an antenna inan FEM, in accordance with one or more embodiments of the invention.

An integrated circuit in accordance with aspects of the presentdisclosure can be employed in essentially any application and/orelectronic system where high-frequency power semiconductor devices(e.g., RF power amplifiers) are employed. Suitable systems and devicesfor implementing embodiments of the invention may include, but are notlimited to, portable electronics (e.g., cell phones, tablet computers,etc.). Systems incorporating such integrated circuits are consideredpart of this invention. Given the teachings of the present disclosureprovided herein, one of ordinary skill in the art will be able tocontemplate other implementations and applications of embodiments of theinvention.

The illustrations of embodiments of the invention described herein areintended to provide a general understanding of the various embodiments,and they are not intended to serve as a complete description of all theelements and features of apparatus and systems that might make use ofthe circuits and techniques described herein. Many other embodimentswill become apparent to those skilled in the art given the teachingsherein; other embodiments are utilized and derived therefrom, such thatstructural and logical substitutions and changes can be made withoutdeparting from the scope of this disclosure. The drawings are alsomerely representational and are not drawn to scale. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Embodiments of the invention are referred to herein, individually and/orcollectively, by the term “embodiment” merely for convenience andwithout intending to limit the scope of this application to any singleembodiment or inventive concept if more than one is, in fact, shown.Thus, although specific embodiments have been illustrated and describedherein, it should be understood that an arrangement achieving the samepurpose can be substituted for the specific embodiment(s) shown; thatis, this disclosure is intended to cover any and all adaptations orvariations of various embodiments. Combinations of the aboveembodiments, and other embodiments not specifically described herein,will become apparent to those of skill in the art given the teachingsherein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof. Terms such as “upper,” “lower,” “front” and “back” are used toindicate relative positioning of elements or structures to each otherwhen such elements are oriented in a particular manner, as opposed todefining absolute positioning of the elements.

The corresponding structures, materials, acts, and equivalents of allmeans or step-plus-function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the various embodiments has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the forms disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope and spirit of the invention. The embodiments were chosen anddescribed in order to best explain the principles of the invention andthe practical application, and to enable others of ordinary skill in theart to understand the various embodiments with various modifications asare suited to the particular use contemplated.

The abstract is provided to comply with 37 C.F.R. § 1.72(b), whichrequires an abstract that will allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the appended claims reflect,inventive subject matter lies in less than all features of a singleembodiment. Thus the following claims are hereby incorporated into theDetailed Description, with each claim standing on its own as separatelyclaimed subject matter.

Given the teachings of embodiments of the invention provided herein, oneof ordinary skill in the art will be able to contemplate otherimplementations and applications of the techniques of embodiments of theinvention. Although illustrative embodiments of the invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that embodiments of the invention are not limited to thoseprecise embodiments, and that various other changes and modificationsare made therein by one skilled in the art without departing from thescope of the appended claims.

What is claimed is:
 1. An integrated circuit, comprising: asemiconductor substrate of a first conductivity type; at least onefront-end module (FEM) formed on the substrate, the at least one FEMcomprising: at least one power amplifier (PA) configured for connectionto an antenna without inclusion of a switching element in a transmitsignal path between an output of the PA and the antenna; at least afirst low-noise amplifier (LNA); and a switching circuit coupled in areceive signal path between the antenna and an input of the first LNA,the switching circuit being configured in a first mode to disable the PAand to connect the input of the first LNA to the antenna for receivingsignals from the antenna, the switching circuit being configured in asecond mode to disconnect the input of the first LNA from the antennaand to enable the PA for transmitting signals to the antenna; a firstwell of a second conductivity type formed in the substrate proximate anupper surface of the substrate; and a second well of the firstconductivity type formed within the first well proximate the uppersurface of the substrate, the first well having a depth in the substratethat is greater than a depth of the second well; wherein the switchingcircuit in the at least one FEM comprises: at least a first passtransistor connected between the antenna and the input of the first LNA,the first pass transistor selectively connecting the input of the firstLNA to the antenna as a function of a first control signal; and at leasta first shunt transistor connected between the input of the first LNAand a first voltage source, the first shunt transistor selectivelyconnecting the input of the first LNA to the first voltage source as afunction of a second control signal; and wherein at least one of thefirst pass transistor and the first shunt transistor is formed in thesecond well, a p-n junction between the first and second wellselectrically isolating the at least one of the first pass transistor andthe first shunt transistor from the substrate.
 2. The integrated circuitof claim 1, further comprising: a third well of the second conductivitytype formed in the substrate and proximate an upper surface of thesubstrate, the third well being disposed laterally adjacent to the firstwell and electrically isolated from the first well; and a fourth well ofthe first conductivity type formed within the third well and proximatethe upper surface of the substrate, the third well having a depth in thesubstrate that is greater than a depth of the fourth well; wherein thefirst pass transistor is formed in the second well and the first shunttransistor is formed in the fourth well, p-n junctions between the firstand second wells and between the third and fourth wells, respectively,electrically isolating the first pass transistor and the first shunttransistor from the substrate and from one another.
 3. The integratedcircuit of claim 1, wherein the at least one FEM further comprises atleast a second shunt transistor connected to an input of the at leastone PA, and wherein the switching circuit is configured in the firstmode to activate the second shunt transistor to thereby disable the PA,the switching circuit being configured in the second mode to deactivatethe second shunt transistor to thereby enable the PA for transmittingsignals to the antenna.
 4. The integrated circuit of claim 1, wherein inthe first mode, the first pass transistor is turned on and the firstshunt transistor in the switching circuit is turned off, and in thesecond mode, the first pass transistor is turned off and the first shunttransistor in the switching circuit is turned on.
 5. The integratedcircuit of claim 4, wherein in the first mode, the first and secondcontrol signals are configured such that the first pass transistor isturned on after the first shunt transistor in the switching circuit isturned off, and in the second mode, the first and second control signalsare configured such that the first pass transistor is turned off beforethe first shunt transistor in the switching circuit is turned on.
 6. Theintegrated circuit of claim 1, wherein the at least one PA in the atleast one FEM comprises a bias circuit, the bias circuit beingselectively enabled as a function of a third control signal, and whereinin the first mode, the first pass transistor is turned on, the firstshunt transistor in the switching circuit is turned off and the biascircuit is disabled, and in the second mode, the first pass transistoris turned off, the first shunt transistor in the switching circuit isturned on, and the bias circuit is enabled.
 7. The integrated circuit ofclaim 6, wherein in the first mode, the first, second and third controlsignals are configured such that the first pass transistor is turned onafter the first shunt transistor in the switching circuit is turned offand the bias circuit is disabled, and in the second mode, the first,second and third control signals are configured such that the first passtransistor is turned off before the first shunt transistor in theswitching circuit is turned on and the bias circuit is enabled.
 8. Theintegrated circuit of claim 1, wherein each of at least a subset of thetransistors in the switching circuit in the at least one FEM comprisesan n-type laterally- diffused metal-oxide semiconductor (LDMOS)transistor.
 9. The integrated circuit of claim 1, wherein the at leastone FEM further comprises: at least one filter circuit operativelycoupled between the antenna and at least one of the PA and the firstLNA; and an impedance matching network connected to the antenna andconfigured to match an impedance of the PA for thereby increasing powerdelivery to the antenna.
 10. The integrated circuit of claim 1, whereinthe switching circuit in the at least one FEM comprises: a plurality ofpass transistors connected in series between the antenna and the inputof the first LNA, the pass transistors selectively connecting the inputof the first LNA to the antenna as a function of at least first controlsignals; and a plurality of shunt transistors, each of the plurality ofshunt transistors coupled either between adjacent pass transistors and afirst voltage source or between the input of the first LNA and the firstvoltage source, the shunt transistors selectively connecting acorresponding node in the switching circuit to the first voltage sourceas a function of at least second control signals.
 11. The integratedcircuit of claim 1, wherein an output of the at least one PA in the atleast one FEM is connected directly to the antenna.
 12. The integratedcircuit of claim 1, wherein the at least one PA in the at least one FEMcomprises a multi-stage PA including a plurality of PA stages connectedtogether in series in the transmit signal path.
 13. The integratedcircuit of claim 12, wherein the at least one FEM is configured suchthat in the first mode, at least a given one of the plurality of PAstages connected to the antenna is disabled to thereby disable the PAfrom transmitting signals to the antenna, and in the second mode, eachof the plurality of PA stages is enabled.
 14. The integrated circuit ofclaim 1, wherein the at least one FEM further comprises a plurality ofLNAs formed on the substrate, the plurality of LNAs having respectivereceive signal paths associated therewith, each of the LNAs having aninput that is selectively connected to the antenna through the switchingcircuit, the switching circuit being configured in the first mode todisable the PA and to connect at least one of the plurality of LNAs tothe antenna for receiving signals from the antenna, the switchingcircuit being configured in the second mode to disconnect the respectiveinputs of the plurality of LNAs from the antenna and to enable the PAfor transmitting signals to the antenna.
 15. The integrated circuit ofclaim 14, wherein the at least one FEM is configured such that in thefirst mode, the switching circuit connects at least two of the pluralityof LNAs to the antenna.
 16. The integrated circuit of claim 1, whereinthe at least one FEM further comprises a second LNA, the second LNAhaving an input coupled with the switching circuit, the switchingcircuit being configured in the first mode to disable the PA, to connectthe input of the first LNA to the antenna for receiving signals from theantenna, and to disconnect the input of the second LNA from the antenna,the switching circuit being configured in the second mode to disconnectthe inputs of the first and second LNAs from the antenna and to enablethe PA for transmitting signals to the antenna, the switching circuitbeing configured in a third mode to disable the PA, to connect the inputof the second LNA to the antenna for receiving signals from the antenna,and to disconnect the input of the first LNA from the antenna.
 17. Theintegrated circuit of claim 1, wherein the at least one FEM furthercomprises at least one shunt device connected to an input of the atleast one PA, the shunt device being external to the PA and beingconfigured to selectively shunt the input of the PA to ground as afunction of at least a first control signal supplied to the at least oneshunt device, and wherein the switching circuit in the at least one FEMis configured in the first mode to supply the at least first controlsignal for activating the at least one shunt device to thereby disablethe PA, the switching circuit being configured in the second mode tosupply the at least first control signal for deactivating the at leastone shunt device to thereby enable the PA for transmitting signals tothe antenna.